Maternal smoking during pregnancy is associated with infant morbidity and mortality and behavioral deficits in older children. Despite pervasive sanctions against smoking, 13-30% of women continue to smoke leading to greater than one in ten infants exposed. Given continued high rates of maternal smoking, novel approaches are needed to protect infants from the consequences of exposure. The proposed study offers a paradigm shift in approaches to maternal smoking by defining novel and potentially reversible biological pathways to adverse behavioral outcomes from maternal smoking. Specifically, we provide the first rigorous test of the proposal that, similar to maternal stress, maternal smoking programs the offspring hypothalamic pituitary adrenocortical (HPA) axis leading to persistent neurobehavioral deficits. We further propose that HPA programming by maternal smoking will be mediated by alterations in the maternal-placental neuroendocrine milieu. Preliminary work by our group has shown effects of maternal smoking on markers of maternal-placental HPA dysregulation (maternal cortisol, placental 112 hydroxysteroid dehydrogenase type 2 (112 HSD 2) gene expression), and between these markers and infant neurobehavioral deficits. Epigenetic regulation of the glucocorticoid receptor (GR) gene has emerged as an additional critical mediator of intergenerational transmission of maternal stress in animal models, but little human research. Epigenetic mechanisms involve inherited changes in phenotype that do not involve alterations in DNA sequence, thus offering unprecedented potential for modification with novel therapeutic targets. Our preliminary work revealed the first evidence of epigenetic regulation of placental GR following exposure to maternal smoking. The proposed study is an intensive investigation of pathways to infant neurobehavioral deficits from maternal smoking. The study involves prospective examination of smokers and controls over pregnancy followed by developmentally-sensitive measures of infant neurobehavior and cortisol reactivity at 1 and 6 months and measurement of novel markers of maternal-placental HPA and epigenetic regulation. Our goals are: 1) to characterize effects of maternal smoking on infant neurobehavior and cortisol reactivity at 1 and 6 months, 2) to test the possibility that maternal smoking programs the HPA axis via regulation of maternal glucocorticoids and placental 112 HSD2 and that these changes influence infant neurobehavior/cortisol reactivity, 3) to test the hypothesis that maternal-placental HPA regulation is mediated by epigenetic regulation of GR, and 4) to explore sex differences in proposed pathways. To our knowledge, our study is the first to investigate HPA and epigenetic pathways to adverse outcomes from maternal smoking in humans. Our study is distinguished by its focus on novel pathways and innovative methods pioneered by our group. Results from the proposed study will elucidate the earliest biomarkers of risk from maternal smoking and may lead to the development of novel therapeutic targets to protect infants whose mothers continue to smoke.